Properly unwrapping UV
First of all in object mode select your wall and apply rotation and scale (Ctrl A) so that your object has rotation 0,0,0 and scale 1,1,1: it's a good practice that affects also UV unwrapping.

Then in edit mode select all and remove doubles (there are 4 doubles that confuse the algorithm), then - in wireframe view - select the little face at the bevel zone between the mesh and her mirrored side and delete it.

Then select all the edges you want to act as seams, in order to preserve the visible faces (front and lateral) without seams.

In the pictures my example.

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